I would keep it simple and give it some compost, composted manure or even cottonseed meal. Hydrangeas do not have the same requirements for fertilizer as roses and will not necessarily have the huge growth spurt that roses have when you fertilize them. It seems that they take what they need and that is it; similar to azaleas and rhododendros who do not consume much fertilizer either.

Thanks for your answer. That does sound like a good idea. I didn't know whether climbers, being more sun/heat tolerant, have different feeding requirements. I hope it grows a lot this summer.

Luis' advice is good - hydrangeas really do not require much in the way of fertilizer. I can say that other than mulching with an organic, compost-based mulch, I never fertilize my climbing hydrangea.

It is also important to understand that fertilizing to promote vigorous growth is not advised. You only want to supply whatever nutrients might be missing from the soil, if any. Plants manufacture their own food via photosynthesis and attempting to stimulate rapid growth through unnecessary fertilization can result in growth that is excessively vulnerable to pests and diseases. Unfortunately, this is exactly the opposite of what fertilizer manufactures would lead you to believe - the "more fertilizer, the bigger and healthier the plants" concept that is simply not borne out by reality. But then they are really in the business of selling their product, not passing on what is best for the plant or good gardening practices. It is all marketing hype.

Climbing hydrangeas just establish and grow rather slowly. It can be as long as five years or more before they start producing blooms. Patience is definitely a virtue in this regard :-)